Helical Nanographenes Containing an Azulene Unit: Synthesis, Crystal Structures, and Properties. Issue 14 (3rd February 2020)

• Record Type: Journal Article
• Authors: Ma, Ji; Fu, Yubin; Dmitrieva, Evgenia; Liu, Fupin; Komber, Hartmut; Hennersdorf, Felix; Popov, Alexey A.; Weigand, Jan J.; Liu, Junzhi; Feng, Xinliang
• Is Part Of: Angewandte Chemie international edition. Volume 59:Issue 14(2020)
• Page Start: 5637
• Page End: 5642
• Publication Date: 2020-02-03
• Subjects: azulene -- helicenes -- nanographenes -- polycyclic aromatic hydrocarbons -- Scholl reaction; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201914716
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Three unprecedented helical nanographenes (1, 2, and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X‐ray crystallographic analysis. The embedded azulene unit in 2 possesses a record‐high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis‐spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps (2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in‐situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties. Abstract : An odd contribution : Azulene‐embedded helical nanographenes with global aromaticity are synthesized by a Scholl‐type cyclization. X‐ray crystallographic analysis clearly reveals the formation of an azulene unit in the helical π‐system. The embedded azulene core adopts a highly twisted conformation and is less aromatic than pristine azulene.